The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
As semiconductor manufacturing processes become more miniaturized and complex, the causes for failure within semiconductor die are also becoming more complex. Depending on the nature of failure modes, various non-destructive methods may be used to locate defects, such as for example current time domain reflectometry (CTDR), infrared imaging technology, scanning acoustic microscopy (SAM), and x-ray computed tomography. More recently, thermal laser stimulation methods such as optical beam induced resistance change (OBIRCH) have been used in addition to or instead of some of the above methods. Failure analysis by OBIRCH involves scanning metal lines of an integrated circuit (IC) with a laser in the infrared region. The laser locally heats the metal lines. Areas of the metal lines containing a defect will heat differently than normal areas, resulting in resistance changes in those defect areas. By applying a constant voltage, areas having resistance changes will result in current changes, which can in turn be plotted in a brightness image, where areas of different current show up as “hot spots” of different pixel brightness. The brightness image can be overlaid onto the IC drawing so that areas on the IC which have defects show up as hot spots.
One problem is that the resolution of OBIRCH is around 5 μm, owing for example to the infrared wavelength of the laser. As the bit line pitch is on the order of 50 nanometers, conventional OBIRCH methods do not provide sufficient resolution with respect to the bit line defect location.